[Coco] The MOOH board (MMU/SPI) for Dragon/CoCo1/2

[Mark J. Blair]

> On Mar 18, 2018, at 09:55, Gene Heskett <gheskett at shentel.net> wrote:
> And while I have made a half hearted start, I keep running out 
> of drawbar actuator ideas, and real estate to make it all fit without 
> getting in the machines way. The drawbar needs at least 60 lb/ft of 
> torque, which the spindle drive doesn't have even if the drawbolt is 
> locked and the spindle motor run in the correct direction. Such torque 
> needs will likely strip the teeth off the 2 speed gear change gears as 
> they are plastic in this Chinese mill. So the spindle quill would need 
> to be pinned to lock, and the top of the bolt driven by a separate 
> mechanism.  That complicates things considerably.  Sigh...

I have an old Bridgeport R2E4 CNC mill with their BOSS 9 controller. Four 68k processors: One runs the whole show, with another dedicated to each axis.

It doesn't have an automatic tool changer, but it does have an aftermarket add-on manual quick-change drawbar. There's an assembly added up on top that runs the drawbar, driven by an air impact wrench mecahnism. It's controlled by a pneumatic directional control valve with two push buttons, and has an extra mechanism to disengage it from the drawbar when it's not operating. It's been a long time since I've looked at it, but I seem to recall that the mechanism works something like a Bendix drive in an engine starter. But I guess it can't be exactly like an automotive starter, since it needs to work in both directions.

I think the machine already had an automatic spindle brake for the add-on toolpost drive to work against. It's been several years since I've used the mill (it's currently still in pieces from my last move... sigh), but as I recall, when the spindle stops, it *stops*, braking firmly enough to be able to wrench on tool holders while they're in the spindle. No plastic gears in that machine, either! Axis ballscrews are driven through wide timing belts by DC motors, each with both a tachometer generator and an optical encoder. Spindle speed control is managed with a continuously variable transmission.

As long as we're drifting off the original topic anyway, I've recently acquired a couple of old military surplus AN/UGC-137 intelligent communications terminals (think of a glass teletype with local message editing and storage capabilities). I'm planning to reverse-engineer the beasts for fun and to figure out how to make it do tricks. It's based on a whole pile of MC6809 and MC68701 (EPROM version of MC6801) processors, so there's your weak CoCo tie-in. They also use removable bubble memory cartridges for non-volatile storage, and the first place I ever learned about bubble memory was in a magazine article about making a bubble memory cartridge for the CoCo, way back in the day. Now, after 35 years or so, I finally have some bubble memory to play with, and it's even in an MC6809 based system!

-- 
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/